I use a system helmet (LS2 -ff386) with Scala G4 intercom for my iPhone and connection to my Wife.
Sub 50 km/t in the city, I might ride with the helmet open faced, but with the sun visor down to protect my eyes from bugs and other issues, under normal situations, I use the helmet closed and visor ALMOST closed, just a couple of millimeter opening. This because I need the extra air vent.
If I could get enough air, and keep the silence , I would ride with the visor closed. I do get some calls on the road.